Wireless communications device with impairment compensation and associated methods

ABSTRACT

A mobile wireless communications device includes a transceiver, an auxiliary receiver and a controller. The transceiver includes a transmitter and a receiver. The transmitter upconverts a transmit baseband modulated signal and generates an RF modulated signal having a transmit impairment. The auxiliary receiver is coupled to the transmitter and downconverts the RF modulated signal and generates a receive baseband modulated signal having a receive impairment therein spectrally separated from the transmit impairment. The controller is coupled to the transmitter and the auxiliary receiver and estimates the transmit impairment while ignoring the receive impairment based on comparing the transmit baseband modulated signal with the receive baseband modulated signal. The controller generates an impairment compensation signal based upon the estimated transmit impairment.

TECHNICAL FIELD

The present disclosure relates to the field of wireless communications,and more particularly, to compensation of a transmitter within a mobilewireless communications device.

BACKGROUND

In general, undesired or non-ideal characteristics, such as DC offsetand in-phase/quadrature-phase (IQ) imbalance, degrade performance ofmobile transceivers. The DC offset is the effect of self mixing by amixer, and occurs when a signal of a local oscillator (LO) returns afterleaking toward an antenna or when a radio frequency (RF) modulationsignal input through the antenna is leaked to the local oscillator.Another way to create DC offset is through an inherent offset in theamplifiers due to imbalances. If the DC offset is amplified byamplifiers in the signal path, then this way may saturate a basebandcircuit.

The IQ imbalance is caused when the phase difference between thein-phase (I) channel signal and the quadrature-phase (Q) channel signalgenerated in an oscillator of a wireless transmitter is not 90 degrees.The IQ imbalance can be reduced by designing mixers of the I channeldemodulator and the Q channel demodulator to be precisely 90 degrees inphase delay (i.e., orthogonal) to each other. However, designing themixers so that there is precisely a 90 degrees phase difference to eachother is not practical over process and temperature variations. This isbecause in the layout, the I and Q paths to the mixers traversedifferent lengths despite the best effort of keeping everythingsymmetrical. This is especially true for multi-band systems. An IQimbalance increases the Bit Error Rate (BER), thereby degrading theperformance of the wireless transceiver.

One approach for compensating DC offset and IQ imbalance betweenorthogonal signals within in a mobile wireless communications device isdisclosed in U.S. Pat. No. 7,782,928. The communications device includesa transmitter that functions as a signal generator, and a receiver thatfunctions as a response characteristic detector. A baseband processorapplies predefined test signals to the transmitter, receives the testsignals returning from the receiver, and compensates the imbalance andDC offset for the transmitter side and the receiver side by using thetest signals.

Another approach for compensating DC offset and IQ imbalance betweenorthogonal signals within in a mobile wireless communications device isdisclosed in U.S. Published Patent Application No. 2009/0262861. Abaseband processor generates an I baseband signal and a Q basebandsignal. A direct up-converter is coupled to the baseband processor, andcombines the I and Q baseband signals with an RF carrier signal togenerate an RF output signal. The antenna is coupled to the directup-converter, and transmits the RF output signal. An impairmentdetection and compensation feedback circuit is coupled to the RF outputsignal, and the I and Q baseband signals. The impairment detection andcompensation feedback circuit down-converts the RF output signal togenerate an intermediate frequency (IF) signal, measures as least onesignal impairment in the IF signal, and pre-distorts the I and Qbaseband signals to compensate for the measured signal impairment.

Yet another approach is disclosed in the article titled “Calibration ofDirect-Conversion Transceivers” by Debaille, IEEE Journal of SelectedTopics in Signal Processing, Volume 3, No. 3, June 2009. To enableseparation of the impairments caused by the transmitter and thereceiver, their local oscillators are operated at slightly differentfrequencies. Compensation is then based on using a dual-tone calibrationsignal, such as a standard compliant OFDM modulated preamble, wherein amulti-tone symbol travels through a transceiver configured in loop-back.The compensation is performed by pre- and post-compensating the basebandsignal of the transmitter and receiver respectively.

Even in view of the above approaches for compensating DC offset and IQimbalance between orthogonal signals within in a mobile wirelesscommunications device, there is still a need to improve suchcompensation. A drawback of the above approaches is that data cannot betransmitted by the transmitter when being trained or compensated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a mobile wireless communicationsdevice in accordance with one exemplary aspect.

FIG. 2 is a more detailed schematic block diagram of the mobile wirelesscommunications device illustrated in FIG. 1.

FIG. 3 is a schematic block diagram of another embodiment of thenon-directional coupler illustrated in FIG. 2.

FIG. 4 is a spectral plot of the transmit baseband modulated signalprovided by the data modulator in accordance with one exemplary aspect.

FIG. 5 is a spectral plot of the RF modulated signal having the transmitimpairment as provided by the transmitter in accordance with oneexemplary aspect.

FIG. 6 is a spectral plot of the receive baseband modulated signalhaving the receive impairment spectrally separated from the transmitimpairment as provided by the auxiliary receiver in accordance with oneexemplary aspect.

FIG. 7 is a more detailed schematic block diagram of the mobile wirelesscommunications device illustrated in FIG. 1.

FIG. 8 is a spectral plot of a complex filter applied to the receivebaseband modulated signal in accordance with one exemplary aspect.

FIG. 9 is a spectral plot of a selective filter applied to the positivefrequencies in the receive baseband modulated signal in accordance withone exemplary aspect.

FIG. 10 is a spectral plot of selective filters applied to the positiveand negative frequencies in the receive baseband modulated signal inaccordance with one exemplary aspect.

FIG. 11 is a flowchart illustrating a method for operating a mobilewireless communications device while taking into account impairmentcompensation in accordance with one exemplary aspect.

FIG. 12 is a constellation plot of a signal with zero EVM in accordancewith one exemplary aspect.

FIG. 13 is a constellation plot of a signal with a non-zero EVM inaccordance with one exemplary aspect.

FIG. 14 is a flowchart illustrating a method for operating a mobilewireless communications device while taking into account performanceevaluation in accordance with one exemplary aspect.

FIG. 15 is a front view of a mobile wireless communications device inaccordance with another exemplary aspect.

FIG. 16 is a schematic block diagram illustrating additional componentsthat may be included in the mobile wireless communications deviceillustrated in FIG. 15.

DETAILED DESCRIPTION

The present description is made with reference to the accompanyingdrawings, in which various embodiments are shown. However, manydifferent embodiments may be used, and thus the description should notbe construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete. Like numbers refer to like elements throughout and primenotations are used to indicate similar elements in alternativeembodiments.

In accordance with one exemplary aspect, a mobile wirelesscommunications device comprises a portable housing, and a transceiver,an auxiliary receiver and a controller all carried by the portablehousing. The transceiver may comprise a transmitter and a receiver, andthe transmitter may be configured to upconvert a transmit basebandmodulated signal and generate an RF modulated signal having a transmitimpairment. The auxiliary receiver may be coupled to the controller andconfigured to downconvert the RF modulated signal and generate a receivebaseband modulated signal having a receive impairment therein spectrallyseparated from the transmit impairment.

The controller may be coupled to the transmitter and the auxiliaryreceiver. The controller may be configured to estimate the transmitimpairment while ignoring the receive impairment based on comparing thetransmit baseband modulated signal with the receive baseband modulatedsignal, and generate a transmit impairment compensation signal basedupon the estimated transmit impairment.

The controller may be configured to perform the estimating andgenerating during operation of the transmitter while transmitting data.This advantageously allows the compensation of the transmitter to beperformed in the background during regular operation of the transmitter.

The transmit baseband modulated signal may comprise an in-phase (I)component signal and a quadrature-phase (Q) component signal. Anon-directional coupler may be carried by the portable housing andcoupled between the transceiver and the auxiliary receiver. An antennamay be carried by the portable housing and coupled to the transceiver.

The transmitter may comprises a transmit impairment compensatorconfigured to compensate the transmit baseband modulated signal based onthe transmit impairment compensation signal. The controller isconfigured to perform the comparing in a plurality of iterations todetermine difference values therebetween. The transmit impairmentcompensator may be configured to perform the compensation by iterativelyadding correction values to the transmit baseband modulated signal tocompensate for the difference values from the plurality of iterations.

The controller may be configured to calculate the correction valuesbased on a least means square (LMS) algorithm. The controller maycomprise a delay circuit configured to delay the transmit basebandmodulated signal so that the transmit baseband modulated signal and thereceive baseband modulated signal match up in time when compared.

The transmitter may comprise a transmit local oscillator operating at afirst frequency, and the auxiliary receiver may comprise a receive localoscillator operating at a second frequency offset from the firstfrequency. This advantageously allows the transmitter impairment to beseparated in the frequency domain from the impairments added in theauxiliary receiver. Otherwise, if the transmitter and the auxiliaryreceiver were to use the same local oscillator with no frequency offset,then the IQ imbalance of the auxiliary receiver becomesindistinguishable from the IQ imbalance introduced in the transmitter.The DC offsets introduced in the auxiliary receiver also becomeindistinguishable from the offsets introduced in the transmitter.

The transmitter may be configured to operate in a dual-mixer mode, andthe auxiliary receiver may be configured to operate in a single-mixermode. The modulated signal may be generated at a carrier frequency. Thetransmitter may comprise a first mixer stage operating at anintermediate frequency, and a second mixer stage operating at thecarrier frequency minus the intermediate frequency. The auxiliaryreceiver may comprise a mixer stage operating at the carrier frequency.

Alternatively, the transmitter may be configured to operate in asingle-mixer mode, and the auxiliary receiver may be configured tooperate in the dual-mixer mode (i.e., a two step down-conversion to DC).The transmitter may comprise a mixer stage operating at the carrierfrequency. The auxiliary receiver may comprise a first mixer stageoperating at the carrier frequency minus the intermediate frequency, anda second mixer stage operating at the intermediate frequency preferablyin the digital domain.

A method aspect is for operating a mobile wireless communications deviceas described above. The method may comprise generating a transmitbaseband modulated, and operating the transmitter to upconvert thetransmit baseband modulated signal and generate an RF modulated signalhaving a transmit impairment. The auxiliary receiver may be operated todownconvert the RF modulated signal and generate a receive basebandmodulated signal having a receive impairment therein spectrallyseparated from the transmit impairment. The controller may be operatedto estimate the transmit impairment while ignoring the receiveimpairment based on comparing the transmit baseband modulated signalwith the receive baseband modulated signal, and to generate a transmitimpairment compensation signal based upon the estimated transmitimpairment. The transmitter may compensate the transmit basebandmodulated signal based on the compensation signal.

After the above described impairment has been estimated and compensationhas been applied to a mobile wireless communications device, performanceof the device can then be monitored, and if necessary, tuned to improveperformance. This is advantageously performed without the need forexternal test equipment. However, this exemplary aspect can be practicedwithout having to perform the above described impairment estimation andcompensation.

In accordance with this exemplary aspect, the transmitter may beconfigured to be selectively operable based on a control signal betweena single-mixer mode (zero-IF direct up-conversion) and a dual-mixer mode(low-IF direct up-conversion) to upconvert the transmit basebandmodulated signal and generate an RF modulated signal having the transmitimpairment. The auxiliary receiver may be configured to be selectivelyoperable based on the control signal between the single-mixer mode(zero-IF direct conversion), when the transmitter is in the dual-mixermode, and the dual-mixer mode (low-IF direct conversion), when thetransmitter is in the single-mixer mode, to downconvert the RF modulatedsignal and generate a receive baseband modulated signal having thetransmit impairment. All four combinations of using the zero-IF orlow-IF modes between the transmitter and receiver are all valid modes ofoperation.

In particular, the auxiliary receiver may be selectively operable in thesingle-mixer mode when the transmitter is selectively operable in thedual-mixer mode, and in the dual-mixer mode when the transmitter isselectively operable in the single-mixer mode. The operation is toensure that the impairments added by the transmitter are frequencyseparated from the impairments added in the auxiliary receiver. This isso that compensations can be correctly computed by comparing thereference transmit signal with the part of the signal received from theauxiliary receiver that isolates the signal that results from theimpairments created in the transmitter or the auxiliary-receiver.

The controller may be configured to compare the transmit basebandmodulated signal to the transmit impairment to determine an errordifference therebetween, and generate the control signal based on theerror difference.

The error difference may correspond to an error vector magnitude (EVM),and the controller may be configured to derive a signal-to-noise ratio(SNR) of the RF modulated signal based on the EVM. The controller may beconfigured to estimate a bit error rate (BER) of the RF modulated signalbased on the SNR.

When the transmitter is operating in the dual-mixer mode, this isadvantageous when transmitting data at a high output power whilefighting VCO pulling. However, if performance of the transmitter beginsto decline, then the transmitter may be selected to operate in thesingle-mixer mode while transmitting at low power. In this mode, thetransmitter may be recompensated if necessary so that the performance ofthe transmitter is improved.

If the auxiliary receiver is operating in the dual-mixer mode, then thisis advantageous for estimating the impairments created in thetransmitter and in the auxiliary receiver, which in turn may be usedwhen compensating the transmitter or the auxiliary receiver. Once theimpairments have been compensated in the auxiliary receiver, then theauxiliary receiver may advantageously be operated in the single-mixermode.

For example, the transmitter may be selectively configured to operate inthe dual-mixer mode and may comprise a first mixer stage operating atthe intermediate frequency, and a second mixer stage operating at thecarrier frequency minus the intermediate frequency. In this case, theauxiliary receiver may be selectively configured to operate in thesingle-mixer mode and may comprise a mixer stage operating at thecarrier frequency. Alternatively, the transmitter may be operated inlow-IF mode to allow frequency separation of transmit and receiveimpairments (i.e., DC offsets and I/Q imbalance).

For another example, the transmitter may be selectively configured tooperate in the single-mixer mode and may comprise a mixer stageoperating at the carrier frequency. In this case, the auxiliary receivermay be selectively configured to operate in the dual-mixer mixer and maycomprise a first mixer stage operating at the carrier frequency minus anintermediate frequency, and a second mixer stage operating at theintermediate frequency.

A method aspect is for operating a mobile wireless communications deviceas described above. The method may comprise selectively operating thetransmitter based on a control signal between a single-mixer mode and adual-mixer mode to upconvert a transmit baseband modulated signal andgenerate an RF modulated signal having a transmit impairment. Theauxiliary receiver may be selectively operated based on the controlsignal between the single-mixer mode and the dual-mixer mode todownconvert the RF modulated signal and generate a receive basebandmodulated signal having the transmit impairment. The transmitter may beoperated in the dual-mixer mode when transmitting very high outputpower, in which case, VCO pulling degrades the output spectral purity.

The auxiliary receiver may be selectively operable in the single-mixeror dual-mixer mode when the transmitter is selectively operable in thedual-mixer mode, and in the dual-mixer mode when the transmitter isselectively operable in the single-mixer mode. The method may furthercomprise operating the controller to compare the transmit basebandmodulated signal to the transmit impairment to determine an errordifference therebetween, and generate the control signal based on theerror difference.

Referring initially to FIG. 1, a mobile wireless communications device10 comprises a portable housing 12, a transceiver 14 comprising atransmitter 16 and a receiver 18 carried by the portable housing, and anantenna 19 coupled to the transceiver. An auxiliary receiver 20 iscarried by the portable housing 12 and is coupled to the transmitter 16.The auxiliary receiver 20 may also be referred to as a feedbackreceiver. The controller 22 is carried by the portable housing 12 and iscoupled to the transmitter 16 and to the auxiliary receiver 20. Thecontroller 22 includes an impairment module 24 to estimate impairmentwithin the transmitter 16, and to generate a transmit impairmentcompensation signal based on the estimated transmit impairment.

More particularly, the transmitter 16 is configured to upconvert atransmit baseband modulated signal and generate an RF modulated signalhaving the transmit impairment therein. Typically, analog circuitry inthe transmit chain within the transmitter 16 causes the transmitimpairment.

The auxiliary receiver 20 is configured to downconvert the RF modulatedsignal and generate a receive baseband modulated signal having a receiveimpairment therein spectrally separated from the transmit impairment.Typically, analog circuitry in the receive chain within the auxiliaryreceiver 20 causes the receive impairment. The controller 22 isconfigured to estimate the transmit impairment while ignoring thereceive impairment based on comparing the transmit baseband modulatedsignal with the receive baseband modulated signal, and generate thetransmit impairment compensation signal based upon the estimatedtransmit impairment. The transmit impairment compensation signal isprovided to the transmitter.

The auxiliary receiver 20 is an additional receiver that is includedwithin the mobile wireless communications device 10 that mayadvantageously be used to service the needs of the transmitter 12.Estimation and compensation for IQ imbalance and DC offset are examplesof servicing the needs of the transmitter 16, as will be appreciated bythose skilled in the art.

The auxiliary receiver 20 can be of lower performance as compared to themain receiver 18 since it is primarily designed to serve thetransmitter. For example, the auxiliary receiver 20 does not need tohave a high dynamic range like the main receiver 18, nor a highselectivity. Alternatively, the main receiver 18 may operate in place ofthe auxiliary receiver to provide the same function if the standardallows for a time-division duplex (TDD) operation in which the mainreceiver is generally not needed when the transmitter 16 is operating.

The auxiliary receiver 20 is configured to have an independent,dedicated phase-locked loop that is offset from the local oscillatoroperating the transmitter 16. This advantageously allows the transmitterimpairment to be separated in the frequency domain from the impairmentsadded in the auxiliary receiver 20. If the main receiver 18 is a TDDreceiver to provide the function of the auxiliary receiver 20, then thisimplies that it should operate with its own independent PLL.

Otherwise, if the transmitter 16 and the auxiliary receiver 20 were touse the same local oscillator with no frequency offset, then the IQimbalance of the auxiliary receiver becomes indistinguishable from theIQ imbalance introduced in the transmitter. The DC offsets introduced inthe auxiliary receiver 20 also become indistinguishable from the offsetsintroduced in the transmitter 16.

The mobile wireless communications device 10 may be a multi-frequencyband device that operates over a 2.4 GHz frequency band (i.e.,approximately 2.4 to 2.483 GHz) and over a 5 GHz frequency band (i.e.,approximately 4.9 to 6 GHz), for example. Depending on the intendedapplication, the mobile wireless communications device 10 may operateover other frequency bands, as readily appreciated by those skilled inthe art.

The mobile wireless communications device 10 will now be discussed ingreater detail with reference to FIG. 2. The transmitter 16 includes adata modulator 30 that modulates data to be transmitted and provides adigital in-phase (I) component signal and a digital quadrature-phase (Q)component signal to the transmitter 16.

The transmitter 16 is configured as a low-IF transmitter (i.e.,dual-mixer mode) since it includes a two mixer stages, wherein the firstmixer stage 40 operates at an intermediate frequency (IF), and thesecond mixer stage 50 operates at the desired carrier frequency offsetby the intermediate frequency so that the resulting frequency of the RFmodulated signal to be transmitted is at the desired carrier frequency.The dual-mixer mode allows the output spectrum of the transmitter 16 tobe offset with respect to the frequency of the local oscillatorassociated with the second mixer stage. This significantly helps toreduce VCO pulling by the power amplifier 64.

The first mixer stage 40 includes a pair of mixers 42 a, 42 b thatreceive the digital I and Q component signals and multiplies them by acomplex exponential 44. The first mixer stage 40 translates the digitalI and Q component signals in frequency to an intermediate frequencyω_(IF). The translated digital I and Q component signals are applied todigital-to-analog converters 46 a, 46 b. The resulting translated analogI and Q component signals are then filtered using low pass filters 48 a,48 b.

The second mixer stage 50 includes a pair of mixers 52 a, 52 b thatreceive the translated analog I and Q component signals at theintermediate frequency ω_(IF), and I and Q local oscillator signals at afrequency of ω_(c)−ω_(IF) from a transmit phase-locked loop 54. Thetransmit phase-locked loop 54 includes a local oscillator 56 and avoltage controlled oscillator 58 coupled thereto. The frequencyω_(c)−ω_(IF) is the desired carrier frequency ω_(c) offset by theintermediate frequency ω_(IF). The output of the second mixer stage 50is the RF modulated I component signal and the RF modulated Q componentsignal at the desired carrier frequency ω_(c).

A summer 60 sums the outputs of the second mixer stage 50 to provide theRF modulated signal at the carrier frequency ω_(c). The low-IFtransmitter architecture shown in FIG. 2 allows the local oscillator 56of the transmit phase-locked loop 54 to be placed at an offset to thecarrier frequency of the modulated signal.

The modulated signal from the summer 60 is amplified with a pre-poweramplifier (PPA) 62. The pre-power amplifier 62 is used to insure thatthere is enough power to drive the power amplifier (PA) 64. The outputof the power amplifier 64 is coupled to the antenna 19. The output ofthe power amplifier 64 has a spectrum that is offset with respect to thefrequency of the local oscillator 56. This significantly helps to reduceVCO pulling by the power amplifier 64.

Reducing VCO pulling is a design challenge for deep sub-microntransceivers 14 that have small feature sizes and cannot provide enoughisolation between the output of the power amplifier 64 and the VCO 58.The output of the power amplifier 64 may be up to 27 dBm, for example.At high output powers, various couplings in the transceiver 14 and thecircuit boards therein create an aggressing signal at the VCO 58 which“pulls” the VCO, thereby forcing the local oscillator 56 to momentarilyfollow the output of the power amplifier 64 and violate phase noisespecifications, before the transmit phase-locked loop 54 fights it off.

The low-IF transmitter advantageously helps to reduce VCO pulling byoffsetting the frequency of the local oscillator 56 ω_(c)−ω_(IF) and thefrequency of the RF modulated signal ω_(c) output by the power amplifier64. The more separated in frequency these signals are, then the more theVCO pulling is reduced. However, there is now an added requirement thatthe RF modulated signal output from the power amplifier 64 still needsto meet certain design specifications, such as a high IQ balance and DCoffset. This means that impairments in the transmitter 16 need toestimated and compensated. Typically, the analog circuitry in thetransmit chain within the transmitter 16 causes such impairments.

If the IF frequency is selected to be zero, the first mixer 42 a/42 bdoes not up-convert, but rather multiplies the baseband I/Q signals withunity. The second mixer 52 a, 52 b up-converts using the localoscillator frequency ω_(c)−ω_(IF)=ω_(c)−0=ω_(c). Hence, in thisselection, the transmitter 16 becomes single-mixer transmitter with zeroIF frequency.

During background calibration, the transmitter 16 is configured as azero-IF transmitter (i.e., single-mixer mode) wherein the first mixerstage 40 operates at an intermediate frequency (IF) of zero, and thesecond mixer stage 50 operates at the desired carrier frequency. Thesingle-mixer mode directly places the output spectrum of the transmitter16 at the desired carrier frequency. This mode is turned on for powerlevels of the transmitter where VCO pulling is not a concern. This modeis used to adaptively update the degradation estimates in the backgroundin anticipation of the low-IF mode, when it will be turned on for higheroutput powers.

As will now be explained, a time domain approach is used to estimate thetransmit impairment (e.g., IQ imbalance and DC offset) in thetransmitter 16. This requires the RF modulated signal with the transmitimpairment generated by the transmitter 16 for transmission to be feedback to the auxiliary receiver 20.

The auxiliary receiver 20 is configured to downconvert the RF modulatedsignal having the transmit impairment. Since the auxiliary receiver 20also includes analog circuitry in the receive chain, a receiveimpairment is added along with the transmit impairment. The receiveimpairment is to be spectrally separated from the transmit impairment.

The RF modulated signal having the transmit impairment from thetransmitter 16 is provided to the auxiliary receiver 20 using anon-directional coupler 70 coupled between the pre-power amplifier 62and the power amplifier 64. Alternatively, a non-directional coupler 74may be coupled between the power amplifier 64 and the antenna 19.

An advantage of using a non-directional coupler 72, 74 is that it canoperate over a wide band of operation, and its performance remains wellcontrolled over temperature and frequency changes. In addition, anon-directional coupler 70, 74 prevents the local oscillator of theauxiliary receiver 20 from parasitically coupling to the output of thetransmitter 16.

A switch in the auxiliary receiver 20 is operated to select whichnon-directional coupler 70, 74 is to provide the RF modulated signalhaving the transmit impairment. The selected non-directional coupler 70,74 directs a small amount of signal energy from the antenna to theauxiliary receiver 20.

In one embodiment, the non-directional coupler 70 comprises a signalpath conductor 71 and a feedback path conductor 72 inductively coupledthereto, and the non-directional coupler 74 also comprises a signal pathconductor 75 and a feedback path conductor 76 inductively coupledthereto.

In another embodiment, as illustrated in FIG. 3, the non-directionalcoupler 70′ is a resistor 72′ directly connected to the transmitteroutput node and feeds to the LNA 82′ of the auxiliary receiver 20′.Since the impedance looking into the PPA output and PA input is two 50ohm impedances in parallel, a 500-10,000 ohm resistance can be used todirectly connect the LNA input to this output node. Alternatively, thePA output can also drive the LNA input. Any of the two drivers can beselected by using a switched LNA or a switch before the LNA that canprovide the desired connection under software control.

Instead of using a non-directional coupler, it is possible to use adirectional coupler. The use of a directional coupler provides a steadyfeedback signal independent of the VSWR variation at the antenna or thePPA load. However, a non-directional coupler is preferred because it iswideband and simpler to implement.

The RF modulated signal having the transmit impairment is received bythe switch 80. The switch 80 is operated by the controller 22. The RFmodulated signal is provided to a low noise amplifier 82. The output ofthe low noise amplifier 82 is provided to a first mixer stage 90. Theauxiliary receiver 20 is configured as a O-IF receiver (i.e.,single-mixer mode) since the transmitter 16 is configured as a low-IFtransmitter (i.e., dual-mixer mode). This means that the second mixerstage 104 is not needed and is selectively set to a value of 1 (i.e.,e^(j0)) by the controller 22. In a different embodiment, the switch 80can be combined with the LNA to provide two input pairs, one of which isselected under software control.

The mixer stage 90 includes a pair of mixers 92 a, 92 b that receive theRF modulated signal having the transmit impairment, and I and Q localoscillator signals from a receive phase-locked loop 94. The receivephase-locked loop 94 includes a local oscillator 96 and a voltagecontrolled oscillator 98 coupled thereto.

The frequency of the RF modulated signal having the transmit impairmentis ω_(c). Since the frequency of the local oscillator 56 in thetransmitter 16 is ω_(c), the frequency of the local oscillator 96 in theauxiliary receiver 20 is ω_(c)−ω_(IF). As noted above, the auxiliaryreceiver 20 is configured to have an independent, dedicated phase-lockedloop 96 that is offset from the local oscillator 56 operating thetransmitter 16. This advantageously allows the transmitter impairment tobe separated in the frequency domain from the impairments added in theauxiliary receiver 20.

The output of the mixers 92 a, 92 b provide receive modulated analog Iand Q component signals at the intermediate frequency ω_(IF). Thesesignals are provided to low pass filters 100 a, 100 b and then toanalog-to-digital converters 102 a, 102 b so that the receive basebandmodulated analog I and Q component signals are now receive basebandmodulated digital I and Q component signals at the intermediatefrequency ω_(IF). The receive baseband modulated digital I and Qcomponent signals at the intermediate frequency ω_(IF) include thereceive impairment spectrally separated from the transmit impairment.These signals are passed through the mixers 106 a, 106 b. The secondmixer stage 104 translates this complex signal to zero-IF in a seconddown-conversion operation by frequency T_(IF).

Spectral plots of the transmit baseband modulated signal, the RFmodulated signal and the receive baseband modulated signal will now bediscussed in reference to FIGS. 4-6. The transmit baseband modulatedsignal as provided by the data modulator 30 to the transmitter 16 isindicated by reference 118 in FIG. 4. The transmit baseband modulatedsignal is also referred to as the reference signal since is does notinclude impairments from the transmitter 16.

The RF modulated signal which is the transmit baseband modulated signalhaving been upconverted by the transmitter 16 is indicated by reference119 in FIG. 5. The RF modulated signal includes the transmit basebandmodulated signal and the impairments introduced by the transmitter 16.The RF modulated signal is also provided to the auxiliary receiver 20.Within the RF modulated signal 119, the transmit baseband modulatedsignal is indicated by reference 120, an image of the transmit basebandmodulated signal is indicated by reference 122. The image of thetransmit baseband modulated signal 122 folds around the carrierfrequency of the transmitter (f_(c,TX)), and the transmit localoscillator feedthrough (LOFT) 124 appears as a tone that can causeviolation of the origin offset error at low output powers.

The receive baseband modulated signal as provided by the auxiliaryreceiver 20 is indicated by reference 129 in FIG. 6. The receivebaseband modulated signal includes the transmit baseband modulatedsignal as well as the receive impairment spectrally separated from thetransmit impairment. Since the receiver is a low-IF receiver, thedegradations due to the auxiliary receiver 20 as indicated by references130, 132 are now spectrally offset from the degradations due to thetransmitter 16. The degradations due to the transmitter 16 are indicatedby references 134, 135. The transmit baseband modulated signal isindicated by reference 136.

In the illustrated example of the mobile wireless communications device10 in FIG. 2, the transmitter 16 comprises two mixer stages 40, 50, andthe auxiliary receiver 20 also comprises two mixer stages 90, 104.During calibration both of the mixer stages 90, 104 are operational fortranslating the received baseband modulated signal. The first mixerstage 40 in the transmitter 16 is selectively set to a value of 1 (i.e.,e⁰) by the controller 22.

Only one of the mixer stages 50 in the transmitter 16 may be operationalfor translating the transmit baseband modulated signal, as illustratedin FIG. 7. The other mixer stage 40 is not needed and is selectively setto a value of 1 (i.e., e⁰) by the controller 22.

When the transmitter 16 is operating in the dual-mixer mode, this helpsto fight VCO pulling when the power amplifier 64 is operating at highpower. When the power amplifier 64 is operating at low power, then thetransmitter 16 may be configured to operate in the single-mixer mode. Ineither case, the local oscillator 96 in the auxiliary receiver 20 isoffset from the local oscillator 66 in the transmitter 16.

Compensation of the transmitter 16 will now be discussed in greaterdetail. The controller 22 is configured to perform the estimating duringoperation of the transmitter 16 while transmitting data. Special tonesor calibration signals are not required. Instead, data transmittedduring normal operation of the transmitter 16 is used.

As illustrated in FIG. 2, the controller 22 is coupled to the output ofthe data modulator 30 and to the output of the auxiliary receiver 20.The controller 22 receives the transmit baseband modulated signal, asindicated by reference 118 in FIG. 4. The transmit baseband modulatedsignal is also referred to as the reference signal since it does notinclude impairments from the transmitter 16.

The controller 22 also receives the receive baseband modulated signal asprovided by the auxiliary receiver 20, as indicated by reference 129 inFIG. 6. The receive baseband modulated signal includes the transmitbaseband modulated signal as well as the receive impairment spectrallyseparated from the transmit impairment.

The controller 22 includes a delay circuit 150 configured to delay thetransmit baseband modulated signal so that this signal and the receivebaseband modulated signal match up in time when compared. The delaycircuit 150 may be configured to implement a fixed delay correspondingto inherent delays of the transmitter 16 and the auxiliary receiver 30,and a variable delay corresponding to variable environmental conditions.The variable delay accounts for environmental conditions, such asoperating temperature variations, for example. In particular, the analogsections within the transmitter 16 and the auxiliary receiver 20 areeffected by temperature variations.

The impairment module 24 within the controller 22 estimates impairmentwithin the transmitter 16, and generates an impairment compensationsignal for the transmitter based on the estimated transmit impairment.The transmitter 16 includes a transmit impairment compensator 34configured to compensate the transmit baseband modulated_signal based onthe compensation signal. The transmit impairment compensator 34 ispositioned between the data modulator 30 and the first mixer stage 40.Alternatively, the transmit impairment compensator 34 may be implementedwithin the controller itself if the transmitter chain is routed throughthe controller 22.

The impairment module 24 is configured to estimate the transmitimpairment by comparing the transmit baseband modulated signal with thereceive baseband modulated signal while ignoring the receive impairment.The impairment module 24 performs the comparing in a plurality ofiterations to determine difference values therebetween. The transmitimpairment compensator 34 then performs the compensation by iterativelyadding correction values, as provided by the compensation signal, to thetransmit baseband modulated signal to compensate for the differencevalues from the plurality of iterations. A least means square (LMS)algorithm may be used to determine the compensation values, for example.

The impairment module 24 may be implemented within a processor, forexample, as appreciated by those skilled in the art. The impairmentmodule 24 is configured to estimate IQ imbalance and local oscillatorfeedthrough, and will be discussed as an inverse system modelingproblem. Output of the impairment module 24 is modeled based on thefollowing equation:

y(n)=w ₁ ·x(n)+w ₂ ·x*(n)+dc

The transmit baseband modulated signal is represented by x(n), and animage of the transmit baseband modulated signal is represented by x*(n).Weighting or gain values are represented by w₁ and w₂, and are complexnumbers. A dc term is also included in the equation.

The weighting value w₁ embodies the path gain from the digitalrepresentation of the ideal transmit baseband modulated signal to thedigitized receive baseband modulated signal at the output of theauxiliary receiver 20. The absolute value of w₁ is the ratio w₂/w₁ anddc/w₁ that needs to receive the appropriate compensation. Thecompensation to w₁ can be normalized without any loss in fidelity of thecompensation. It is important to keep the feedback gain high enough suchthat the digital representation of the receive baseband modulated signalfrom the auxiliary receiver 20 spans almost the full dynamic range ofthe analog-to-digital converters 102 a, 102 b. This provides a highsignal to noise ratio and allows a high image and local oscillatorfeedthrough to be achieved. The error signal is given based on thefollowing equation:

e(n)=d(n)−y(n)=d(n)−w ₁ ·x(n)−w ₂ ·x*(n)−dc

The desired response is represented by d(n). Using the steepest descentapproach, the following is obtained:

$\mspace{79mu} {{\frac{\partial\;}{\partial w_{1}}{e(n)}} = {{- \text{?}}(n)}}$$\mspace{79mu} {{\frac{\partial\;}{\partial w_{2}}{e(n)}} = {- {x(n)}}}$$\mspace{79mu} {{\frac{\partial\;}{\partial{dc}}{e(n)}} = {- 1}}$?indicates text missing or illegible when filed

Therefore, the update equations are as follows:

w ₁(n+1)=w ₁(n)+μ·e(n)·x*(n)

w ₂(n+1)=w ₂(n)+μ·e(n)·x(n)

dc(n+1)=dc(n)+μ·e(n))

On convergence, the error signal is driven to zero so that y(n)=d(n) ina mean square sense. Now, the inverse function has been calculated.

The transmit impairment estimation may include the use of a veryselective low pass filter. The low pass filter may be a single stage andbe programmable with the following transfer function:

${H_{2}(z)} = \frac{2^{- M}}{1 - {\left( {1 - 2^{- M}} \right)z^{- 1}}}$

where M is programmable from 0-10. This filter has unity gain at dc. Thereference signal for determining the IQ imbalance and dc offsetsintroduced by the receiver may be determined using synthesis. The outputsignal of the impairment module 24 may be synthesized as follows:

$\mspace{79mu} {{y(n)} = {{x(n)} + {{\frac{w_{2}}{w_{1}} \cdot \text{?}}(n)} + \frac{dc}{w_{1}}}}$?indicates text missing or illegible when filed

This creates the reference signal centered at dc. This signal isup-converted to the low pass filter to create the reference signalneeded to compute the impairments introduced in the auxiliary receiver20.

Operation of the impairment module 24 may be simplified based onadditional filtering of the receive baseband modulated signal beforebeing provided as an input to the impairment module 24. In the aboveembodiment, the controller 20 typically includes a filter 151 that needsto be large enough to pass the transmit impairment portion of the signalwhile rejecting the receive impairment portion of the signal. After thesecond down-conversion in the auxiliary receiver 20, the transmitimpairment signal 136 centers at DC and can be isolated from thereceiver impairments using a lowpass filter. This filter 151, isolatesthe transmit impairment signal so that the controller 22 can compare itto the ideal reference signal (output of 150) and estimate theimpairments using the LMS algorithm or a different method.

In another embodiment of this filter 151, a complex filter may be used.The complex filter has a response 153 as illustrated in FIG. 8. Thecomplex filter is used to select the positive frequencies, which arethen provided to the impairment module 24 after translating the positivefrequencies at zero-IF.

As an alternative to the complex filter, a lossy integrator may filterthe zero-IF down-converted signal which is output from the seconddown-conversion stage 104 in the auxiliary receiver 20. This filter canbe implemented very simply to have a cascade of filters, each with asingle-pole IIR response. This filter implementation is inexpensive, yetvery powerful. The filtering operation modifies the in-band frequencycomponents of the auxiliary receiver output signal. Hence, it may becompared to a similarly modified reference signal (i.e., the idealtransmit signal from the data modulator 30). The filter 157 is identicalto the filter 151, and hence modifies the reference signal in the sameway as the filter 151 modifies the output of the auxiliary receiveroutput signal. The same LMS update equations can be used to estimate theimpairments caused in the transmitter.

The impairment module 24 may also be used to estimate and generate areceive impairment compensation signal to correct for impairments withinthe auxiliary receiver 20. The auxiliary receiver 20 includes a receiveimpairment compensation signal for the receive impairment compensator 37within the auxiliary receiver 20.

The receive impairment compensator 37 is positioned at the output of thelast mixing stage. Alternatively, the receive impairment compensator 34may be implemented within the controller itself if the receive chain isrouted through the controller 22. As discussed above for the estimationand compensation of the transmit impairment, an inverse system modelingis also used for the receive impairment

As discussed above, complex filtering and very selective complex lossyintegrator filtering may be used to provide inputs to the impairmentmodule 24. In addition, the receive impairment may be estimated withoutrequiring the transmit baseband modulated signal. Instead, a veryselective complex lossy integrator may be used to extract a portion ofthe signal spectrum centered at the positive intermediate frequency, anda very selective complex lossy integrator may be used to extract aportion of the signal spectrum centered at the negative intermediatefrequency. The complex lossy integrators have responses 155, 159 asillustrated in FIG. 10.

A flowchart 200 illustrating a method for operating a mobile wirelesscommunications device 10 while taking into account impairmentcompensation will now be discussed in reference to FIG. 11. From thestart (Block 202), the method comprises generating a transmit basebandmodulated at Block 204. The transmitter 16 is operated at Block 206 toupconvert the transmit baseband modulated signal and generate an RFmodulated signal having a transmit impairment. The auxiliary receiver 20is operated at Block 208 to downconvert the RF modulated signal andgenerate a receive baseband modulated signal having a receive impairmenttherein spectrally separated from the transmit impairment. Thecontroller 22 is operated at Block 210 to estimate the transmitimpairment while ignoring the receive impairment by comparing thetransmit baseband modulated signal with the receive baseband modulatedsignal, and is operated at Block 212 to generate an impairmentcompensation signal for the transmitter 16 based upon the estimatedtransmit impairment. The transmitter 16 compensates the transmitbaseband modulated signal at Block 214 based on the compensation signal.The method ends at Block 216.

After the above described impairment has been estimated and compensationhas been applied to the mobile wireless communications device 10,performance of the device can then be monitored, and if necessary, tunedto improve performance. This is advantageously performed without theneed for special test signals or external test equipment. Performancemonitoring and tuning may be performed during operation of thetransmitter while transmitting data. However, this exemplary aspect canbe practiced without having to perform the above described impairmentestimation and compensation, as readily appreciated by those skilled inthe art.

As illustrated in FIG. 2, a performance monitoring module 35 is includedin the controller 22 along with the impairment module 24. Thetransmitter 16 is selectively operable based on a control signal betweenthe single-mixer mode and the dual-mixer mode to upconvert a transmitbaseband modulated signal and generate an RF modulated signal having atransmit impairment.

The auxiliary receiver 20 is also selectively operable based on thecontrol signal between the single-mixer mode, when the transmitter 16 isin the dual-mixer mode, and the dual-mixer mode, when the transmitter isin the single-mixer mode, to downconvert the RF modulated signal andgenerate a receive baseband modulated signal having the transmitimpairment. In particular, the auxiliary receiver 20 is selectivelyoperable in the single-mixer mode when the transmitter 16 is selectivelyoperable in the dual-mixer mode, and in the dual-mixer mode when thetransmitter is selectively operable in the single-mixer mode.

The performance module 25 within the controller 22 compares the transmitbaseband modulated signal to the transmit impairment to determine anerror difference therebetween, and generate the control signal based onthe error difference. The error difference corresponds to an errorvector magnitude (EVM), and the performance module 25 then derives asignal-to-noise ratio (SNR) of the RF modulated signal based on the EVM.

Although not illustrated, the mobile wireless communications device 10may also include an auxiliary transmitter along with the auxiliaryreceiver 20. The auxiliary transmitter may be used for determiningimpairment compensation of the receiver. The same principles discussedherein are equally applicable to the auxiliary transmitter and the mainreceiver 18, as readily appreciated by those skilled in the art.

The EVM is also referred to as a receive constellation error (RCE), andis a measure used to quantify the performance of a digital radiotransmitter or receiver. A signal sent by an ideal transmitter orreceived by a receiver with a zero EVM would have all constellationpoints 240 precisely at the ideal locations, as illustrated in FIG. 12.However, various imperfections in the implementation (such as DC offsetand IQ imbalance) cause the actual constellation points 250 to deviatefrom the ideal locations, as illustrated in FIG. 12. Essentially, EVM isa measure of how far the points are from the ideal locations. Thecontroller 22 is configured to estimate a bit error rate (BER) of the RFmodulated signal based on the SNR.

The RF modulated signal is generated at a carrier frequency, and thetransmitter 16 is selectively configured to operate in the dual-mixermode and comprises a first mixer stage 40 operating at the carrierfrequency minus an intermediate frequency, and a second mixer stage 50operating at the intermediate frequency. In this configuration, theauxiliary receiver 20 is selectively configured to operate in thesingle-mixer mode and comprises a mixer stage 90 operating at thecarrier frequency.

In another configuration, the transmitter 16 is selectively configuredto operate in the single-mixer mode and comprises a mixer stage 50operating at the carrier frequency. The auxiliary receiver 20 isselectively configured to operate in the dual-mixer mixer and comprisesa first mixer stage 90 operating at the carrier frequency minus anintermediate frequency, and a second mixer stage 104 operating at theintermediate frequency.

When the transmitter 16 is operating in the dual-mixer mode, this isadvantageous when transmitting data at a high output power whilefighting VCO pulling. However, if performance of the transmitter 16begins to decline, then the transmitter may be selected to operate inthe single-mixer mode while transmitting at low power. In this mode, thetransmitter 16 may be recompensated if necessary so that the performanceof the transmitter is improved.

If the auxiliary receiver 20 is operating in the dual-mixer mode, thenthis is advantageous for estimating the impairments created in thetransmitter 16 and in the auxiliary receiver, which in turn may be usedwhen compensating the transmitter or the auxiliary receiver. Once theimpairments have been compensated in the auxiliary receiver 20, then theauxiliary receiver may advantageously be operated in the single-mixermode.

As noted above, the performance module 25 is able to derive a SNR of theRF modulated signal based on the EVM. The following ratio provides therelationship between EVM and SNR:

${SNR} \approx \frac{1}{{EVM}^{2}}$

The derived SNR can be used to predict the BER using a waterfall curvefor the corresponding modulation or through a look up table containingentries that specify BER versus SNR. Computation of EVM for thetransmitter 16 and receiver 20 is performed on-the-fly while thetransmitter and receiver function normally. This is useful in assessingif the analog tuning exercised is effective in improving the overallperformance of the transceiver 16.

There are several analog controls that are exercised to control offsets,IQ imbalance, group delay distortion and in-band droop. These arecontrolled by independent algorithms that are implemented in HW or SW ora combination of two. In addition, selection of the transmitter 16between a single-mixer mode and a dual-mixer mode is another approachfor tuning performance of the transmitter. In order for the receiveimpairment to be spectrally spaced from the transmit impairment in thereceive baseband modulated signal, the auxiliary receiver 20 needs tooperate in a mode that is different from the mode of the transmitter 16.

Although not illustrated, the mobile wireless communications device 10may also include an auxiliary transmitter along with the auxiliaryreceiver 20. The auxiliary transmitter may be used for determiningimpairment compensation of the main receiver 18. The same principlesdiscussed herein are equally applicable to the auxiliary transmitter andthe main receiver 18, as readily appreciated by those skilled in theart. For example, the impairments created in the auxiliary transmittercan be separated from the impairments created in the main receiver 18.

EVM calculation will now be discussed. An error vector is a vector inthe I-Q plane between the ideal constellation point and the pointreceived by the receiver. In other words, it is the difference betweenactual received symbols and ideal symbols. The average power of theerror vector, normalized to signal power, is the EVM. A transmitter 16to auxiliary receiver 20 feedback link can be modeled as a basic AWGNchannel. If the received signal is time aligned to the transmittedsignal, the EVM is defined as:

${EVM} = \frac{\frac{1}{N}{\sum\limits_{n = 1}^{N}\; {{S_{{RX},n} - S_{{TX},n}}}^{2}}}{\frac{1}{N}{\sum\limits_{n = 1}^{N}\; {S_{{TX},n}}^{2}}}$

where S_(TX,n) and S_(RX,n) represent the normalized nth transmitted andreceived symbols, respectively. This is calculated as

${EVM}_{RMS} = \sqrt{\frac{{\frac{1}{N}{\sum\limits_{n = 1}^{N}\; \left\lbrack {I_{RK} - I_{TX}} \right\rbrack^{2}}} + \left\lbrack {Q_{RX} - Q_{TX}} \right\rbrack^{2}}{\frac{1}{N}{\sum\limits_{n = 1}^{N}\left\lbrack {I_{TX}^{2} + Q_{TX}^{2}} \right\rbrack}}}$

In the above equation, the received constellation is normalized to thereceived samples while the transmitted constellation is normalized totransmit samples. Therefore, the analog gain is taken out of the EVMestimate. The performance module 25 uses the error samples from an LMSalgorithm as the error vector in the numerator of the EVM estimate afterthe algorithm has converged. This advantageously achieves elimination ofthe IQ imbalance, elimination of offsets from the received samples. Inaddition, the received constellation to the transmit constellation ismatched such that the difference between the two (error vector) isminimum. Achieving normalization operations on receive samples isachieved through gain adjustment (i.e., determining w₁).

The average power of the transmit samples and the error vector arecalculated separately. The two summations (P_(error) and P_(TX)) arereported to the performance module 25, which in turn, estimates the EVM.Percent EVM can then be computed as:

${{EVM}(\%)} = {\sqrt{\frac{P_{error}}{P_{TX}}} \times 100\%}$

If the LMS algorithm is reasonably converged and the average error andsignal powers are computed over sufficiently large number of samples,the signal-to-noise ratio is approximated as:

${SNR} \approx \frac{1}{{EVM}^{2}}$

The BER can be predicted as an appropriate Q-function based on themeasured SNR. BER is traditionally computed on a communication link bydemodulating the received samples and comparing the decisions to thetransmitted samples. In this approach, the BER can be predicted by usinga Q-function implemented with a lookup table combined with interpolationwithout the need for demodulation. In a radio transceiver, the SNR is amore useful metric compared to BER, which is more relevant to assessingthe quality of a complete radio link. Using the SNR, the noise figure ofthe link can be checked to see if is reasonable. Any asymmetry in thenoise power of I and Q errors also indicates imbalance that needs to beadjusted.

A flowchart 300 illustrating a method for operating a mobile wirelesscommunications device 10 while taking into account performanceevaluation will now be discussed in reference to FIG. 14. From the start(Block 302), the method comprises selectively operating the transmitter16 at Block 304 based on a control signal between a single-mixer modeand a dual-mixer mode to upconvert a transmit baseband modulated signal,and generate an RF modulated signal having a transmit impairment. Theauxiliary receiver 20 is selectively operated at Block 306 based on thecontrol signal between the single-mixer mode, when the transmitter 16 isin the dual-mixer mode, and the dual-mixer mode, when the transmitter isin the single-mixer mode, to downconvert the RF modulated signal, andgenerate a receive baseband modulated signal having the transmitimpairment. The method further comprises operating the controller 22 atBlock 308 to compare the transmit baseband modulated signal to thetransmit impairment to determine an error difference therebetween, andgenerate the control signal based on the error difference at Block 310.The method ends at Block 312.

Exemplary components that may be used in various embodiments of theabove-described mobile wireless communications device are now describedwith reference to an exemplary mobile wireless communications device1000 shown in FIGS. 15 and 16.

The mobile wireless communications device 1000 illustratively includes aportable housing 1200, a keypad 1400 and an output device 1600. Theoutput device shown is a display 1600, which may comprise a full graphicLCD. In some embodiments, display 1600 may comprise a touch-sensitiveinput and output device. Other types of output devices may alternativelybe utilized. The keypad 1400 includes a plurality of control keysincluding an “off hook” (i.e., initiate phone call) key 1402, an “onhook” (i.e., discontinue phone call) key 1404, a menu key 1406, and areturn or escape key 1408.

A processing device 1800 is contained within the housing 1200 and iscoupled between the keypad 1400 and the display 1600. The processingdevice 1800 controls the operation of the display 1600, as well as theoverall operation of the mobile device 1000, in response to actuation ofkeys on the keypad 1400 by the user. In some embodiments, keypad 1400may comprise a physical keypad or a virtual keypad (e.g., using atouch-sensitive interface) or both.

The housing 1200 may be elongated vertically, or may take on other sizesand shapes (including clamshell housing structures, for example). Thekeypad 1400 may include a mode selection key, or other hardware orsoftware for switching between text entry and telephony entry.

In addition to the processing device 1800, other parts of the mobiledevice 1000 are shown schematically in FIG. 16. These include acommunications subsystem 1001; a short-range communications subsystem1020; the keypad 1400 and the display 1600, along with otherinput/output devices 1060, 1080, 1100 and 1120; as well as memorydevices 1160, 1180 and various other device subsystems 1201. The mobiledevice 1000 may comprise a two-way RF communications device having voiceand data communications capabilities. In addition, the mobile device1000 may have the capability to communicate with other computer systemsvia the Internet.

Operating system software executed by the processing device 1800 may bestored in a persistent store, such as the flash memory 1160, but may bestored in other types of memory devices, such as a read only memory(ROM) or similar storage element. In addition, system software, specificdevice applications, or parts thereof, may be temporarily loaded into avolatile store, such as the random access memory (RAM) 1180.Communications signals received by the mobile device may also be storedin the RAM 1180.

The processing device 1800, in addition to its operating systemfunctions, enables execution of software applications or modules1300A-1300N on the device 1000, such as software modules for performingvarious steps or operations. A predetermined set of applications thatcontrol basic device operations, such as data and voice communications1300A and 1300B, may be installed on the device 1000 during manufacture.In addition, a personal information manager (PIM) application may beinstalled during manufacture. The PIM may be capable of organizing andmanaging data items, such as e-mail, calendar events, voice mails,appointments, and task items. The PIM application may also be capable ofsending and receiving data items via a wireless network 1401. The PIMdata items may be seamlessly integrated, synchronized and updated viathe wireless network 1401 with the device user's corresponding dataitems stored or associated with a host computer system.

Communication functions, including data and voice communications, areperformed through the communications subsystem 1001, and possiblythrough the short-range communications subsystem. The communicationssubsystem 1001 includes a receiver 1500, a transmitter 1520, and one ormore antennas 1540 and 1560. In addition, the communications subsystem1001 also includes a processing module, such as a digital signalprocessor (DSP) 1580, and local oscillators (LOs) 1601. The specificdesign and implementation of the communications subsystem 1001 isdependent upon the communications network in which the mobile device1000 is intended to operate. For example, a mobile device 1000 mayinclude a communications subsystem 1001 designed to operate with theMobitex™, Data TAC™ or General Packet Radio Service (GPRS) mobile datacommunications networks, and also designed to operate with any of avariety of voice communications networks, such as AMPS, TDMA, CDMA,WCDMA, PCS, GSM, EDGE, etc. Other types of data and voice networks, bothseparate and integrated, may also be utilized with the mobile device1000. The mobile device 1000 may also be compliant with othercommunications standards such as GSM, 3G, UMTS, 4G, etc.

Network access requirements vary depending upon the type ofcommunication system. For example, in the Mobitex and DataTAC networks,mobile devices are registered on the network using a unique personalidentification number or PIN associated with each device. In GPRSnetworks, however, network access is associated with a subscriber oruser of a device. A GPRS device therefore utilizes a subscriber identitymodule, commonly referred to as a SIM card, in order to operate on aGPRS network.

When required network registration or activation procedures have beencompleted, the mobile device 1000 may send and receive communicationssignals over the communication network 1401. Signals received from thecommunications network 1401 by the antenna 1540 are routed to thereceiver 1500, which provides for signal amplification, frequency downconversion, filtering, channel selection, etc., and may also provideanalog to digital conversion. Analog-to-digital conversion of thereceived signal allows the DSP 1580 to perform more complexcommunications functions, such as demodulation and decoding. In asimilar manner, signals to be transmitted to the network 1401 areprocessed (e.g. modulated and encoded) by the DSP 1580 and are thenprovided to the transmitter 1520 for digital to analog conversion,frequency up conversion, filtering, amplification and transmission tothe communication network 1401 (or networks) via the antenna 1560.

In addition to processing communications signals, the DSP 1580 providesfor control of the receiver 1500 and the transmitter 1520. For example,gains applied to communications signals in the receiver 1500 andtransmitter 1520 may be adaptively controlled through automatic gaincontrol algorithms implemented in the DSP 1580.

In a data communications mode, a received signal, such as a text messageor web page download, is processed by the communications subsystem 1001and is input to the processing device 1800. The received signal is thenfurther processed by the processing device 1800 for an output to thedisplay 1600, or alternatively to some other auxiliary I/O device 1060.A device user may also compose data items, such as e-mail messages,using the keypad 1400 and/or some other auxiliary I/O device 1060, suchas a touchpad, a rocker switch, a thumb-wheel, or some other type ofinput device. The composed data items may then be transmitted over thecommunications network 1401 via the communications subsystem 1001.

In a voice communications mode, overall operation of the device issubstantially similar to the data communications mode, except thatreceived signals are output to a speaker 1100, and signals fortransmission are generated by a microphone 1120. Alternative voice oraudio I/O subsystems, such as a voice message recording subsystem, mayalso be implemented on the device 1000. In addition, the display 1600may also be utilized in voice communications mode, for example todisplay the identity of a calling party, the duration of a voice call,or other voice call related information.

The short-range communications subsystem enables communication betweenthe mobile device 1000 and other proximate systems or devices, whichneed not necessarily be similar devices. For example, the short-rangecommunications subsystem may include an infrared device and associatedcircuits and components, or a Bluetooth™ communications module toprovide for communication with similarly-enabled systems and devices.

Many modifications and other embodiments of the disclosure will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the disclosure is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included as readily appreciated by thoseskilled in the art.

1. A mobile wireless communications device comprising: a portablehousing; a transceiver comprising a transmitter and a receiver carriedby said portable housing, said transmitter configured to upconvert atransmit baseband modulated signal and generate an RF modulated signalhaving a transmit impairment; an auxiliary receiver carried by saidportable housing and coupled to said transmitter and configured todownconvert the RF modulated signal and generate a receive basebandmodulated signal having a receive impairment therein spectrallyseparated from the transmit impairment; and a controller carried by saidportable housing and coupled to said transmitter and said auxiliaryreceiver, said controller configured to estimate the transmit impairmentwhile ignoring the receive impairment based on comparing the transmitbaseband modulated signal with the receive baseband modulated signal,and generate a transmit impairment compensation signal based upon theestimated transmit impairment.
 2. The wireless communications deviceaccording to claim 1 wherein said controller is configured to performthe estimating and generating during operation of said transmitter whiletransmitting data.
 3. The wireless communications device according toclaim 1 wherein the transmit baseband modulated signal comprises anin-phase (I) component signal and a quadrature-phase (Q) componentsignal.
 4. The wireless communications device according to claim 1wherein said transmitter comprises a transmit impairment compensatorconfigured to compensate the transmit baseband modulated signal based onthe transmit impairment compensation signal.
 5. The wirelesscommunications device according to claim 4 wherein said controller isconfigured to perform the comparing in a plurality of iterations todetermine difference values therebetween; and wherein said transmitimpairment compensator is configured to perform the compensation byiteratively adding correction values to the transmit baseband modulatedsignal to compensate for the difference values from the plurality ofiterations.
 6. The wireless communications device according to claim 5wherein said controller is configured to calculate the correction valuesbased on a least means square (LMS) algorithm.
 7. The wirelesscommunications device according to claim 1 wherein said controllercomprises a delay circuit configured to delay the transmit basebandmodulated signal so that the transmit baseband modulated signal and thereceive baseband modulated signal match up in time when compared.
 8. Thewireless communications device according to claim 1 wherein saidtransmitter comprises a transmit local oscillator operating at a firstfrequency, and said auxiliary receiver comprises a receive localoscillator operating at a second frequency offset from the firstfrequency.
 9. The wireless communications device according to claim 1wherein said transmitter is configured to operate in a dual-mixer mode;and wherein said auxiliary receiver is configured to operate in asingle-mixer mode.
 10. The wireless communications device according toclaim 9 wherein the RF modulated signal is generated at a carrierfrequency; wherein said transmitter comprises a first mixer stageoperating at an intermediate frequency, and a second mixer stageoperating at the carrier frequency minus the intermediate frequency; andwherein said auxiliary receiver comprises a mixer stage operating at thecarrier frequency.
 11. The wireless communications device according toclaim 1 wherein said transmitter is configured to operate in asingle-mixer mode; and wherein said auxiliary receiver is configured tooperate in a dual-mixer mode.
 12. The wireless communications deviceaccording to claim 11 wherein the RF modulated signal is generated at acarrier frequency; wherein said transmitter comprises a mixer stageoperating at the carrier frequency; and wherein said auxiliary receivercomprises a first mixer stage operating at the carrier frequency minusan intermediate frequency, and a second mixer stage operating at theintermediate frequency.
 13. The wireless communications device accordingto claim 1 further comprising a non-directional coupler carried by saidportable housing and coupled between said transceiver and said auxiliaryreceiver.
 14. The wireless communications device according to claim 1wherein said controller is configured to estimate the receive impairmentbased on comparing the transmit baseband modulated signal after havingbeen compensated with the receive baseband modulated signal, andgenerate a receive impairment compensation signal for said auxiliaryreceiver based upon the estimated transmit impairment; and wherein saidauxiliary receiver comprises a receive impairment compensator configuredto compensate the receive baseband modulated signal based on the receiveimpairment compensation signal.
 15. The wireless communications deviceaccording to claim 1 further comprising an antenna carried by saidportable housing and coupled to said transceiver.
 16. A mobile wirelesscommunications device comprising: a portable housing; a data processorcarried by said portable housing and configured to provide a transmitbaseband modulated signal comprising an in-phase (I) component signaland a quadrature-phase (Q) component signal; a transceiver comprising atransmitter and a receiver carried by said portable housing, saidtransmitter comprising a transmit local oscillator operating at a firstfrequency and configured to upconvert the transmit baseband modulatedsignal and generate an RF modulated signal having a transmit impairment;an auxiliary receiver carried by, said portable housing and coupled tosaid transmitter, and comprising a receive local oscillator operating ata second frequency offset from the first frequency of said transmitlocal oscillator, and configured to downconvert the RF modulated signaland generate a receive baseband modulated signal having a receiveimpairment therein spectrally separated from the transmit impairment; acontroller carried by said portable housing and coupled to saidtransmitter and said auxiliary receiver, said controller configured toestimate the transmit impairment while ignoring the receive impairmentbased on comparing the transmit baseband modulated signal with thereceive baseband modulated signal, and generate a transmit impairmentcompensation signal based upon the estimated transmit impairment; saidtransmitter comprising a transit impairment compensator configured tocompensate the transmit baseband modulated signal based on the transmitimpairment compensation signal.
 17. The wireless communications deviceaccording to claim 16 wherein said controller is configured to performthe estimating and generating during operation of said transmitter whiletransmitting data.
 18. The wireless communications device according toclaim 16 wherein said controller is configured to perform the comparingin a plurality of iterations to determine difference valuestherebetween; and wherein said transmit impairment compensator isconfigured to perform the compensation by iteratively adding correctionvalues to the transmit baseband modulated signal to compensate for thedifference values from the plurality of iterations.
 19. The wirelesscommunications device according to claim 18 wherein said controller isconfigured to calculate the correction values based on a least meanssquare (LMS) algorithm.
 20. The wireless communications device accordingto claim 18 wherein said controller comprises a delay circuit configuredto delay the transmit baseband modulated signal so that the transmitbaseband modulated signal and the receive baseband modulated signalmatch up in time when compared.
 21. The wireless communications deviceaccording to claim 16 wherein the modulated signal is generated at acarrier frequency; wherein said transmitter comprises a first mixerstage operating at an intermediate frequency, and a second mixer stagedownstream from said first mixer stage and operating at the carrierfrequency minus the intermediate frequency; and wherein said auxiliaryreceiver comprises a mixer stage operating at the carrier frequency. 22.The wireless communications device according to claim 16 wherein themodulated signal is generated at a carrier frequency; wherein saidtransmitter comprises a mixer stage operating at the carrier frequency;and wherein said auxiliary receiver comprises a first mixer stageoperating at the carrier frequency minus an intermediate frequency, anda second mixer stage downstream from said first mixer stage andoperating at the intermediate frequency.
 23. The wireless communicationsdevice according to claim 16 further comprising a non-directionalcoupler carried by said portable housing and coupled between saidtransceiver and said auxiliary receiver.
 24. A method for operating amobile wireless communications device comprising a transceivercomprising a transmitter and a receiver, an auxiliary receiver coupledto the transmitter, and a controller coupled to the transmitter and theauxiliary receiver, the method comprising: generating a transmitbaseband modulated signal; operating the transmitter to upconvert thetransmit baseband modulated signal and generate an RF modulated signalhaving a transmit impairment; and operating the auxiliary receiver todownconvert the RF modulated signal and generate a receive basebandmodulated signal having a receive impairment therein spectrallyseparated from the transmit impairment; and operating the controller toestimate the transmit impairment while ignoring the receive impairmentbased on comparing the transmit baseband modulated signal with thereceive baseband modulated signal, and generate a transmit impairmentcompensation signal based upon the estimated transmit impairment. 25.The method according to claim 24 wherein the controller is configured toperform the estimating and generating during operation of thetransmitter while transmitting data.
 26. The method according to claim24 wherein the transmit baseband modulated signal comprises an in-phase(I) component signal and a quadrature-phase (Q) component signal. 27.The method according to claim 24 wherein the transmitter comprises atransmit impairment compensator configured to compensate the transmitbaseband modulated signal based on the transmit impairment compensationsignal.
 28. The method according to claim 27 wherein the controller isconfigured to perform the comparing in a plurality of iterations todetermine difference values therebetween; and wherein the transmitimpairment compensator is configured to perform the compensation byiteratively adding correction values to the transmit baseband modulatedsignal to compensate for the difference values from the plurality ofiterations.
 29. The method according to claim 28 wherein the controlleris configured to calculate the correction values based on a least meanssquare (LMS) algorithm.
 30. The method according to claim 24 furthercomprising delaying the transmit baseband modulated signal so that thetransmit baseband modulated signal and the receive baseband modulatedsignal match up in time when compared.
 31. The method according to claim24 wherein the mobile wireless communications device comprising anon-directional coupler coupled between the transceiver and theauxiliary receiver.
 32. The method according to claim 24 wherein thecontroller is configured to estimate the receive impairment based oncomparing the transmit baseband modulated signal after having beencompensated with the receive baseband modulated signal, and generate areceive impairment compensation signal for the auxiliary receiver basedupon the estimated receive impairment; and wherein the auxiliaryreceiver comprises a receive impairment compensator configured tocompensate the receive baseband modulated signal based on the receiveimpairment compensation signal.